Powertrain systems which incorporate a plurality of torque-generative devices attached to a transmission device have been proposed for use as vehicle propulsion systems. The torque-generative devices typically include internal combustion engines and electrical machines powered using electrical energy storage devices, e.g. high voltage batteries. Torque outputs of the torque-generative devices are combined in the transmission device to supply motive torque to a driveline of the vehicle.
A typical electrically-variable transmission (EVT) splits mechanical power between an input shaft and an output shaft into a mechanical power path and an electrical power path by means of differential gearing. The mechanical power path may include clutches and additional gears. The electrical power path may employ two electrical power units, each of which may operate as a motor or as a generator. The EVT can be incorporated into a propulsion system for a hybrid electric vehicle using an electrical energy storage device. A typical hybrid propulsion system uses electrical energy storage devices and an internal combustion engine as power sources. The batteries are connected with the electrical drive units through an electronic control system which distributes electrical power as required. The control system also has connections with the engine and vehicle to determine operating characteristics, or operating demand, so that the electrical power units are operated properly as either a motor or a generator. When operating as a generator, the electrical power unit accepts power from either the vehicle or the engine and stores power in the battery, or provides that power to operate another electrical device or another electrical power unit on the vehicle or on the transmission.
A benefit of having an electrically-variable transmission incorporating more than one mode of operation is that each mode of operation will generally incorporate at least one mechanical point where one of the electrical power units is stationary, thereby reducing the electrical power input and providing a pure mechanical power flow path which is, of course, more efficient than a pure electrical power flow path.
There is a need to for a method and apparatus to improve torque and power efficiency of a transmission device, to effectively transmit torque from a plurality of torque-generative devices to an output of the transmission, to provide motive torque to a vehicle.